Senior Software Engineer, Add-Ons - Mozilla

Why Mozilla?

Mozilla Corporation is the non-profit-backed technology company that has shaped the internet for the better over the last 25 years. We make pioneering brands like Firefox, the privacy-minded web browser. Now, with more than 225 million people around the world using our products each month, we’re shaping the next 25 years of technology and helping to reclaim an internet built for people, not companies. Our work focuses on diverse areas including AI, social media, security and more.

The Mozilla Corporation is wholly owned by the non-profit 501(c) Mozilla Foundation, meaning we aren’t beholden to any shareholders — only to our mission. Along with thousands of volunteer contributors and collaborators all over the world, Mozillians design, build and distribute open-source software that enables people to enjoy the internet on their terms.

About this team and role

addons.mozilla.org (AMO) is the foundation of the Firefox add-ons ecosystem. It’s a showcase for developers to publish and grow their extensions, and a place of discovery for millions of users who customize Firefox. Behind the scenes are the DevHub, a series of Reviewer tools, and automated moderation systems.

As a Senior Software Engineer, you’ll bring a passion for crafting resilient systems that accelerate our review and moderation teams to provide a first-class experience for Add-on developers. You’ll work closely with engineers, reviewers, developer support, and Add-ons leadership to turn ideas into polished features, modernize the platform and its architecture, and see your work reach millions of people worldwide.

What you’ll do

• Deliver major features and architectural improvements across the Add-ons stack, including automated moderation pipelines, Reviewer tools, and DevHub.
• Help establish and maintain engineering standards across code review, definition of done, production readiness, runbooks, incident response, on-call practices, coding conventions, and infrastructure as code.
• Create robust observability systems and data-backed insights.
• Provide peer feedback, share knowledge and help others grow.
• Build and improve systems that enable Add-ons engineering to safely develop, deploy, observe, and operate production services.
• Improve CI/CD pipelines using declarative, pipeline-as-code approaches that make changes reproducible, testable, and easy to review.
• Deliver work iteratively using a visible backlog, short feedback cycles, retrospectives, and demonstrations to stakeholders.
• Write clear technical documentation, including design notes, Architecture Decision Records, runbooks, and incident write-ups.
• Work effectively in unfamiliar codebases, tracing requests and asynchronous jobs end-to-end to identify improvement opportunities.
• Collaborate with designers, product managers, QA, and community contributors to deliver end-to-end improvements.
• Contribute in the open through pull requests, code reviews, and discussions.
• Feature development: Submission flows, trust and safety signals, DevHub and Reviewer tools modernization.
• AMO application systems: Work within Python/Django, MySQL, React/TypeScript, and asynchronous processing systems.
• Platform reliability: Deployments, monitoring, and incident response.

What you’ll bring

• Strong hands-on experience building and maintaining production applications with Python/Django.
• Experience operating and improving production software systems where reliability and safe delivery matter.
• Strong experience with CI/CD systems and treating pipelines and infrastructure declaratively as code.
• Experience designing or improving automated testing and deployment workflows, including integration testing and staged or progressive delivery.
• Strong understanding of observability as an engineering discipline, including metrics, logging, tracing, service-level objectives, and actionable alerting.
• Experience building or maintaining internal tools or platforms used by other engineering teams.
• Experience defining or improving engineering practices like code review standards, operational readiness, runbooks, and incident response.
• Ability to read and understand unfamiliar codebases and trace application behavior across frontend, backend, asynchronous jobs, data stores, and infrastructure.
• Strong technical writing skills for design documents, ADRs, runbooks, and incident reports.
• Commitment to our values: welcoming differences, being relationship-minded, practicing responsible participation, and having grit.

What you’ll get

• Generous performance-based bonus plans
• Comprehensive medical, dental, and vision coverage
• Generous retirement contributions with 100% immediate vesting
• Quarterly all-company wellness days
• Country-specific holidays plus a birthday day off
• One-time home office stipend
• Annual professional development budget
• Quarterly well-being stipend
• Considerable paid parental leave
• Employee referral bonus program